1. Field of the Invention
The present invention pertains to the field of underground storage caverns which are used for the bulk storage of liquid hydrocarbons, and in particular to the determination of the configuration of such caverns.
2. Description of the Related Art
In the use of underground storage caverns it is important to determine the approximate shape and volume of the cavern. This has heretofore been done by lowering a wireline device into the cavern and using sonic devices to measure distances from the device to the cavern wall. Another technique has been to pump a liquid into the annulus and determine cavern volume by measuring the liquid pressure and volume at the annulus and central tubing at the well surface. Wireline operations are complex, expensive and subject to leakage of gas or liquid from the wellhead or wireline connectors. Prior cavern survey techniques are shown in U.S. Pat. No. 2,792,708, issued May 21, 1957 entitled “Testing Underground Storage Cavities” and U.S. Pat. No. 3,049,920, issued Aug. 21, 1962 entitled “Method of Determining Amount of Fluid in Underground Storage”.